REACTIVITY OF HYDROXYMETHYLATED RESORCINOL COUPLING AGENT AS IT AFFECTS DURABILITY OF EPOXY BONDS TO DOUGLAS-FIR

Epoxy adhesives develop strong bonds to wood, but they lack the struct ural durability to withstand the severe stresses from repeated water s oaking and drying. Research at the Forest Products Laboratory led to a discovery that hydroxymethylated resorcinol (HMR) physicochemically c ouples to both epoxy adhesive and lignocellulosics of wood to produce bonds that are extraordinarily resistant to delamination. The HMR coup ling agent is quite reactive at room temperatures; therefore, the leng th of its reaction time, or the time between preparing the solution an d applying it to the wood surface, strongly influences the durability of adhesion. The experiments in this study defined the optimum range o f reaction time when adhesion is maximum for epoxy bonds to HMR-primed Douglas-fir. Heats of reaction (by differential scanning calorimetry) , molecular-size distribution (by gel permeation chromatography), and chemical structures of HMR (by carbon-13 nuclear magnetic resonance sp ectroscopy) are described for this range of optimum reaction times.